At present, it is known that electrodes for photoelectric transducers such as solar batteries, displaying devices of liquid crystals, and electrodes for touch panels are made using a transparent conductive film of indium tin oxide (ITO: In2O3+SnO2) or tin oxide (SnO2) formed on a transparent substrate such as glass. Especially for use in liquid crystal or electrodes for touch panels, high transmissivity in visible wavelength and optimum surface resistance are demanded. Many studies are made using the glass substrates and resulted in many inventions of multi-layer films that present high transmissivity and optimum surface resistance. However, the glass substrate has a drawback of fragility and big weight, therefore light and no fragile transparent plastic substrate is recently used to form the multi-layer films.
However, the plastic substrate presents low transmissivity since the plastic material is intrinsically less transparent than the glass and the same multi-layer films as on the glass show lower transmissivity than those on the glass. Some trials to improve transmissivity are made by reducing thickness of the conductive film, which is restricted to maintain the demanded resistance. Therefore the plastic base still showed difficulty for the transmissivity in comparison with glass base.
Again, although multi-layer films with antireflection coating of transparent dielectric thin films are effective to improve transmissivity, the coating on the most exterior surface reduces the conductivity of the surface. It may not be used as the electrode board for the liquid crystals.
In order to overcome this difficulty, efforts are paid to reduce the view sense reflection index by 0.1% steps. Publication of Japanese Laid-Open Patent Application (Tokukai Hei6-316442/1994) published a proposal that antireflection films presents high transmissivity while the most exterior surface is covered with conductive film. This invention says that the thickness of the first-layer film is controlled to be λ/4 and the summation of the thickness of the second- and the third-layer films is also controlled to be λ/4, which results in high transmission. This idea has drawback that the thickness of the second layer is restricted by the thickness of the third-layer, which may prevent high transmissivity.
The present invention, considering the former technical difficulties, has objectives to provide a highly transparent baseboard with multi-layer antireflection films under condition of high transmissivity not only on a glass substrate but also on a non-glass transparent substrate with property of conductivity and proper resistance at most exterior surface, transparent touch panel using the transparent baseboard including multi-layer antireflection films, and electronic equipment using this transparent touch panel.